1. Field of Invention
The present invention relates to apparatuses and methods for monitoring, measuring, or analyzing the sag of a weighted material in a drilling fluid.
2. Description of Prior Art
This tester applies to “sagging” of oil well fluids. Sagging is the settling of weighted additives in the wellbore during drilling conditions, as well as times of static activity. This directly applies to dense materials, such as Barite, used in the drilling fluid. These materials serve little purpose other than a weighting agent. The density measurement is the focus of this tester.
Settling or sag is not an issue with vertical or near vertical drilling, but problematic with higher drilling angles. As these modern angles increase, sag becomes more of an obstacle. Sagging can reduce the rate of penetration, fluid flow, and cutting removal. Sag can occur when the flow of the fluid ceases, as when the drill string stops. Sag can also concentrate in one area during this “static” time.
Addressing this concern has been an issue since the 1920s. Many adjustments to fluids have been made in an effort to alleviate this problem. Until now, minimal substantial test data were available for such research. Drilling fluid changes were made based upon guesswork in the field in the past. Data supporting downhole mud density is critical for modern production and performance.
A few types of arrangements have been applied to measure the sag of drilling fluids. In U.S. Pat. No. 6,330,826, an apparatus consists of a conically or frustro-conically shaped inner body; an outer body having an opening with contours closedly matching those of inner body such that in conjunction inner and outer body are separated by an arrow gap defining a conically or fustro-conically volume with a vertex; a motor drive for rotating the inner body with respect to the outer body; and a sampling access to determine the density of said drilling fluid with a localized part of said volume. One of the drawbacks of this setup is that it can not simulate downhole mud conditions which are under high pressure and high temperature. One other drawback of this apparatus is that the inner and outer body shapes are considerably different from the real drilling conditions in which both bore hole and drilling pipe are cylindrical. In U.S. Pat. No. 6,584,833, a device was disclosed for measuring dynamic and static sag of drilling fluids under high temperature and high pressure conditions. One of the drawbacks of this invention is its complexity. It consists of a very complicated testing cell and delicate electronics and control systems. As of 2007, its cost to build is about 8 times of the current invention. Another drawback of this invention is that it is difficult to achieve more than 5,000 psi due to the nature of its design. Because it needs to sense tiny shifts of center of gravity, it can not use a heavy high-pressure vessel. The current invention can easily test samples up to or more than 30,000 psi. Another drawback of this invention is that it is very difficult to operate and difficult to clean due to its many components and complex design.
It is an object of this invention to provide a sag tester wherein dynamic and static sag caused by settling of weighting materials in drilling fluids or other solids bearing fluids can be accurately determined under conditions closely simulating down-hole environments.
It is another object of this invention to provide a sag tester wherein dynamic and static sag of weighting materials in drilling fluids or other solids bearing fluids can be accurately determined under any inclined angle which simulates any high or low angle drilling operation.
It is another object of this invention to provide a sag tester that requires substantially less maintenance work yet meets industry standards of accuracy, reliability, durability, dependability, and ease of cleaning.